The present specification describes electrical/mechanical systems having at least a three point power interface. Referring to FIGS. 1 and 2, an example of such a system comprises one or more linear actuator systems 10 supplied with AC power from an amplifier 34 which is powered by a direct current (DC) power source, for example a battery 11. As described in more detail below, actuator system 10 comprises stator having a set of coil windings and a shaft. The shaft may be a plunger having a set of permanent magnets. A control system defines an electric current pattern to apply to the coil windings to thereby define a magnetic flux density across a gap between the coil windings and a series of magnets on the shaft, thereby generating a force to move the shaft for a moving magnet linear actuator. The shaft's movement with respect to the coils defines an actuator mechanical power, indicated at 2. Power applied to the coils by battery 11 over a DC bus 13 is indicated at 4, and dissipated power (comprised of power dissipated in the coils, core loss in the motor and power electronics loss in the amplifier) is indicated at 6. Power flows 2, 4 and 6 define a three point power interface between actuator system 10 and the world outside the actuator.
As should be understood, the power across the three point power interface must sum to zero, i.e. the power flowing into the actuator system must balance with the power flowing out. As indicated in FIG. 2 and described in more detail below, dissipated power 6 always flows out of the actuator system, whereas each of actuator mechanical power 2 and DC bus power 4 can flow into or out of the actuator system. If a mechanical event occurs that causes a power flow into the actuator that is greater than the dissipated power out of the actuator system, then DC bus power 4 flows out of the actuator onto the DC bus. This is referred to herein as a regeneration event. As should be understood, regeneration can have the effect of applying electric-current back to, and thereby recharging, battery 11 but can damage the battery if the regeneration current is sufficiently high.